Multi-computer systems with a division of functions are known wherein a main computer in normal operation, which is the trouble-free condition, makes available the total computer capacity for the required closed-loop and open-loop control functions. A second computer serves exclusively as an emergency computer and can take over emergency functions in the event that the main computer becomes defective and can thereby maintain at least a limited operation. As long as no disturbance is present, the emergency computer generally remains unused. In such systems, the main computer is in any event monitored. If a suitable monitoring arrangement detects a disturbance or a defect, the emergency computer takes over the tasks of the main computer at least partially or in their entirety.
U.S. patent application Ser. No. 081,459 filed on June 25, 1987 corresponds to PCT/DE86/00407 and is incorporated herein by reference. This application discloses a computer system with two processors for controlling characteristic quantities of an internal combustion engine. Two sensors are provided for the two processors, one of which supplies measured values to the main computer and the other of which supplies measured values to the emergency computer. Both computers are so configured that they can deliver the same processing capacity. However, the emergency function realized here comprises the alternative assignment of sensor signals to the two processors or, more specifically, the alternative assignment of the output signals of both processors to terminal stages in the fail situation.
If monitoring circuits detect disturbances in the corresponding processors, one of the terminal stages influencing the fuel metering is switched off via an AND-gate. However, a teaching is not provided as to how the two processors with primary and emergency functions and having the same capacity can be monitored. This publication especially does not provide any suggestion as to how a plurality of processors can monitor each other when both are utilized for different tasks and under certain circumstances are operated asynchronously.